This invention relates to reactors for generating gases in general and more particularly to an improved reactor useful in generating fuel gases for internal combustion engines through the catalytic conversion of hydrocarbons with a gas containing oxygen at elevated temperatures.
In equipment for carrying out a catalytic conversion for generating a gas in which a starting material in gaseous and/or atomized or evaporated liquid form is converted in a reactor not only the molecular collisions with a catalyst located in the reaction chamber must be considered but in addition all contact of the raw materials and the product gas with the reactor wall which can have catalytic effect must also be considered. In large reactor the ratio of the wall area to the surface area of the catalyst in the reaction chamber usually can be neglected. However, in smaller reactors such as those used in conjunction with internal combustion engines catalytic reactions may occur due to contact with the walls which can lead to the formation of undesired reaction products. As a result, it is particularly important in smaller reactors that such catalytic reactions be prevented.
Smaller sized reactors of the nature being referred to are used, for example, in the process disclosed in U.S. application Ser. No. 439,870 filed Feb. 6, 1974, by Wolfgang Frie et al. and assigned to the same assignee as the present invention, now abandoned in favor of Ser. No. 633,609 filed Nov. 20, 1975. In the disclosed apparatus a liquid fuel hydrocarbon is atomized or evaporated and supplied to the reaction chamber of a reformed gas generator with a gas containing oxygen admixed to it. The mixture is catalytically converted in the reaction chamber into a completely combustible fuel gas, i.e., reformed gas, which has a high octane number. The reformed gas is particularly well suited for the operation of an internal combustion engine since it requires no antiknock agents and the gas burns more completely with additional combustion air than does directly injected liquid fuel. As a result, the exhaust gases of the internal combustion engine operated using the reformed gas will contain considerably fewer harmful emissions than will an internal combustion engine operated directly with liquid fuel.
The oxygen containing gas is supplied only in such amounts as to result in the formation of methane, carbon monoxide and/or hydrogen. In other words, only a partial catalytic oxidation of the fuel takes place. In order to insure that the calorific value of the fuel gas is not reduced too much, the oxygen supply to the gas generator is throttled to an amount far below that required for combustion. It is well known that, in such greatly understoichiometric reactions of hydrocarbons with oxygen, soot formation will occur in the range of thermodynamic equilibrium. Such soot formation inside the reactor can be prevented through the use of suitable reactive fillings. However, danger exists that, at the prevailing temperatures, wall collisions will accelerate the establishment of the thermodynamic equilibrium and promote soot formation. In addition, for reasons of mechanical stability, the reactor housing of a reformed gas generator, particularly where it is to be used in a motor vehicle is normally made of metal or metal alloys such as stainless steel. However, these metals under some circumstances catalytically favor soot formation. Soot may form not only in the reaction chamber itself but also in the pipe lines and other components in which the hot fuel gas makes contact with a wall without the additional supply of oxygen. Furthermore, it must be remembered that only a limited amount of space is available for the installation of a reformed gas generator in a motor vehicle, that such a generator is subjected to mechanical stresses and that the expense of the production and servicing of the motor vehicle should not be increased substantially due to the use of a reformed gas generator. Such generators containing catalyts and having a specially designed wall defining the reaction chamber are known. For example, in a gas generator disclosed in U.S. Pat. No. 1,795,037 the reactants are conducted through metal tubes lined with porous, active graphite in which a catalytic action is described. Another reactor is disclosed in German Pat. No. 720,535, particularly on page 2, lines 17-58. The disclosed reactor is based on the assumption that a metal or metal alloy exists which can be used as a catalyst for the inner lining of the metal tubes. The metal tubes are disposed in a metal housing through which the exhaust gases of the internal combustion flow, the tube inlets followed in the reactor by a distribution zone. In this zone the reactant materials come in contact with the walls of the metal housing and undesired reactions then occur at the walls. Furthermore, there is a danger that adhesion of the catalytic layers at the metal of the tube cannot stand stresses such as those produced by the large temperature changes.
Another reactor disclosed in German Pat. No. 428,157 page 2, lines 32-35 contains metal tubes which are heated by exhaust gases from outside and includes, along with the reactor jacket and feed lines a metal suitable as a catalyst. Here it is also assumed that suitable metals or metal alloys exist. However, for many reactions there is a serious question as to whether or not metallic materials having the required catalytic action and which do not produce undesired byproducts are available.
In view of these various problems, the need for an improved reactor which is particularly useful for forming a fuel gas for internal combustion engines becomes evident.